This invention relates in general to vehicle wheels and in particular to an apparatus and a process for simultaneously spin forming a pair of partial wheel rims.
It is known in the art to fabricate a two piece vehicle wheel by attaching a wheel disc to a separately formed wheel rim. Typically, the wheel disc is cast or forged while the wheel rim is rolled or spun from strip stock. Such two piece wheels are less expensive to manufacture than a cast one piece wheel while permitting use of stylistic designs for the wheel disc. Both the wheel disc and wheel rim can be formed from alloys of the same light weight metal, such as aluminum, magnesium or titanium, or, as a further cost reduction, a wheel disc formed from an alloy of a light weight metal can be attached to a rim rolled from steel. When different metals are used to form the wheel disc and wheel rim, the assembled wheel is commonly called a bimetal wheel.
To further improve the appearance of the wheel, the wheel disc can be formed to include the outboard tire retaining bead. The resulting wheel disc, which is usually called a full face wheel disc, is attached to the outboard end of a partial wheel rim. The attachment can occur at the outboard tire bead seat, the dropwell, or another location. The assembled wheel is often referred to as a full face wheel. When a tire is mounted upon a full face wheel, the joint between the wheel disc and wheel rim is completely hidden and only the wheel disc is visible. A decorative finish is often applied to the face of the wheel disc to further enhance the appearance of the wheel. Examples of typical decorative finishes include metal plating, such as chromium plating, clear coatings and paint.
As described above, the partial wheel rims used to form full face wheels can be spun from a hoop of metal. The spinning process begins by placing the hoop upon a mandrel having the desired shape of the wheel rim. The mandrel is mounted upon a conventional spin forming machine which rotates the mandrel and hoop while rollers are pressed against and traversed axially across the outer surface of the hoop to form a wheel rim. The rollers axially stretch and radially thin the hoop while forcing the hoop to conform to the shape of the mandrel. Usually several axial passes of the roller are required to form the wheel rim. Additionally, a plurality of rollers may be sequentially applied to the hoop to form specific portions of the wheel rim.
Increasingly, vehicle manufactures are requiring wheels designed for specific vehicles. Such wheels can require different wheel rim shapes to accommodate tires designed for the vehicle. Accordingly, in order to efficiently utilize the spin forming machinery, it is often necessary to change the mandrel on a spin forming machine to spin a differently shaped wheel rim.
Referring now to the drawings, there is shown in FIG. 1 a time line for a typical operations sequence for a spin forming machine being utilized to spin two differently shaped wheel rims which is in accordance with the prior art. For illustrative purposes, the wheel rims are designated rim "A", which is spun upon a mandrel A, and rim "B", which is spun upon a mandrel B. Before t.sub.1, mandrel A is mounted upon the spinning machine.
At t.sub.1, a first production run begins with wheel rim A being spun on mandrel A. The first production run continues until t.sub.2, at which time the spin forming machine is stopped. Mandrel A is removed from the spin forming machine and mandrel B is mounted thereon. The time period from t.sub.2 to t.sub.3 is referred to "changeover", or "down", time and, because the spin forming machine is not operating, represents a period of non-production of wheel rims. At t.sub.3, a second production run begins with wheel Rim B being formed upon the spin forming machine. The second production run continues until t.sub.4, when the spin forming machine is again stopped for another changeover period to reinstall mandrel A. The process described above is repeated, beginning at t.sub.5. Accordingly, one complete cycle for the spin forming machine, which extends from t.sub.1 through t.sub.5, includes two production runs and two changeover periods.